The basic cost for a telephone toll call placed between telephone subscribers is typically billed to the subscriber originating the call (originating subscriber). Such a basic cost is the cost that the originator at a wired telephone station would be required to pay for the call if the call were to be completed directly to another wired telephone station terminating the number dialed. The basic cost for each such call is usually a function of the length of time that passes while the originating subscriber is connected to the terminating subscriber. To develop the basic cost, time is divided into predetermined indivisible time periods, typically of identical length and conventionally one minute in length, to which a period cost is assigned and the accumulation of the period costs for each of the indivisible time periods in the call is the basic cost. The period cost is typically expressed as a dollar value. In some systems, however, period costs may be expressed in terms of messages units, where each message unit has an identical fixed unit cost.
It is possible to make a so-called "collect call", i.e., a call for which the billing of the basic cost of the call is reversed, so that the terminating subscriber pays the basic cost of the call. It is also possible for the basic cost to be reversed only for a portion of the time of the call, so that the entire period cost for some of the indivisible time periods are charged to the originating subscriber while the entire period cost for the remaining ones of the indivisible time periods of the call are charged to the terminating subscriber.
In addition to its basic cost, each call may have a set of additional costs. The additional costs in such a set are each allocated, individually, to one of the subscribers on the call. These additional costs represent the costs associated with the particular ones of advanced services beyond the bare minimum basic telephone service provided for the call. For example, a call from New York, N.Y., dialed to a first, fixed, location in East Brunswick (EB), N.J. that is forwarded to a second, fixed, location in Holmdel, N.J. (HO) engenders a cost for forwarding the call from the first location (EB) to the second location (HO) in addition to the basic cost of the call as originally placed from New York, N.Y. to the first location (EB). The basic cost for the call, which is the cost of reaching the first location, is charged to the originating subscriber while any additional cost for the forwarding is borne by the terminating subscriber who activated the forwarding feature. The cost for the forwarding may also be a function of the length of time that passes while the originating subscriber is connected to the terminating subscriber. Similarly, for a non-collect call from a wired telephone to a cellular telephone, the basic cost for the call is borne by the originating subscriber while the additional cost of so-called "air time charges" is borne by the terminating cellular subscriber.